The present invention relates to an underwater low-frequency sound producer using a Langevin-type transducer.
Conventional technology of this type is described in "Tonpilz transducer using TbDyFe Alloy" by Takashi Yoshikawa, et al., in the Report of the Meeting, the Acoustical Society of Japan, October 1991, page 1071, and Japanese Patent Application H2-214687, some of the authors of which are some of the co-inventors of the present application.
A conventional low-frequency transducer (sound source) of this type comprises a rod of a rare earth alloy and masses attached to opposite ends of the rod.
The conventional transmitter disclosed in the above-mentioned publication has a resonant frequency at 840 Hz and an output sound pressure of 148 dB. It is however desired to have a yet lower resonant frequency and yet a larger sound output. To lower the resonant frequency with the above configuration, it is necessary to use a rod of a smaller diameter or to use heavier masses. This however decreases the mechanical strength of the transmitter. Moreover, to further increase the output, the area used for radiating the acoustic wave must be increased. However, this is limited by the configuration of the prior art transducer.